Agent and method for modifying surface layer of cement structures

ABSTRACT

An agent and method for modifying a surface layer of hardened cement structures or substrates with use of the agent which comprises in a specified ratio of an alkali silicate solution and a sodium naphthalenesulfonate-formaldehyde condensate. Said agent has an excellent stability and a remarkable permeability into the cement structure to form a deeper strengthened surface layer thereon.

The present invention relates to an improvement in or relating to anagent and a method for modifying a surface layer of hardened cementstructures or substrates (herein referred to as "cement structure").

Cement materials such as cement, mortar, concrete, calcium silicate andthe like have widely been used in various fields. The structure madefrom such material, however, has innumerable fine bores communicatingwith its outer surface, and thus various alien matters inevitablypenetrate into such bores to that the surface layer is to bedeteriorated with the lapse of years, which is particularly considerableas to the outdoor structures.

In order to prevent such a deterioration, a method has been proposedwherein to impregnate the cement structure with silica sol containing asilica component, an ammonium component and an alkali metal component ina specified mole ratio (Japanese Examined Patent Application Gazette No.19 609/1978). This method has been confirmed useful and actually carriedout to some extent. It is, however, unsatisfactory in that the agentoften cannot sufficiently penetrate into bores of the structure so thatthe depth of the improved layer for preventing deterioration is notinsufficient depending on its components, preparation method, curingmethod, deterioration degree and other factors.

It has also been proposed to use an aqueous solution of lithium silicate(Japanese Examined Patent Application Gazette No. 30 658/1975) but thisis still unsatisfactory by the same reason.

When shock or tension is affected on the surface of cement structure, athin modified surface layer is sometimes damaged to expose thenon-modified layer. Therefore, it is desirous to form the modifiedsurface layer as deep as possible on the hardened structure.

In order to elucidate mechanism of formation of modified layer, thepresent inventors have made experiments on the aforesaid methods inaccordance with disclosures given in said Japanese Examined PatentApplication Gazettes to find that when sodium toluensulfonate,polyoxyethylenenonylphenol ether, sulfonated melamine-formaldehydecondensate or the like commercially available surfactant is added to thesilica sol or lithium silicate solution, the stability of the agent thusobtained is inferior and gelation is often caused, whereby a permeationof the agent into deeper area of the structure is not attained.

The inventors have studied on the properties of agents obtained byvarious combinations of surfactants and silica sol or silicate solution,and finally found that an agent comprising an alkali silicate solutionand a soidum naphthalenesulfonateformaldehyde condensate, is remarkablystable over an extended period of time and has an excellent permeabilityinto the hardened cement structures when applied on the surfacesthereof.

An object of the present invention is, thus, to provide an agent formodifying the surface layer of hardened cement structures, which isimproved in the stability and permeability so as to satisfactorilyprevent deterioration thereof.

Another object of the invention is to provide a method for modifying thesurface layer of hardened cement structures over a sufficient depth byapplying the agent.

A still other object of the invention is to provide a method forrepairing the deteriorated surface layer of cement structures, byapplying the agent on the deteriorated surface of the structure, dryingthe treated structure, applying a freshly prepared cement material onthe treated surface of said structure, and then curing the appliedcement material.

According to the invention, the agent comprises 100 parts by weight ofan alkali silicate solution and 0.01 to 5 parts by weight of acondensate of sodium naphthalensulfonate and formaldehyde, in which saidalkali silicate solution has a SiO₂ /M₂ O mole ratio of 1 to 50, whereinM represents an alkali metal atom, or a substituted or unsubstitutedammonium cationic radical, and has a SiO₂ content of 1 to 50 weight %.

Further, according to the invention, a modified surface layer is formedon a cement structure over a sufficient depth by a method of applying onand impregnating into the surface of said structure with said agent, andthen leaving to stand or positively drying the thus treated structure.

Still further, according to the invention, repairing of a deterioratedsurface layer of cement structure is attained by a method of furtherapplying a freshly prepared cement material on said dried surface, andthen curing the applied cement material.

The term, "alkali silicate solution" to be used in the specification andClaims designates an aqueous solution of one or more alkali silicates ora liquid wherein stably dispersed fine particles of colloidal silicashall partially co-exist with said dissolved silicates.

A mixture of water with a water soluble organic solvent may also be usedas the medium of the solution. Among the alkali silicates, there may bementioned alkali metal silicates such as lithium silicate, potassiumsilicate, sodium silicate, cesium silicate or the like, and substitutedor unsubstituted ammonium silicates. There may be listed, as examples ofsubstituted or unsubstituted ammoniums, NH₄, CH₃ NH₃, (CH₃)₂ NH₂, (CH₃)₂(C₂ H₄ OH)₂ N, (C₂ H₄ OH)₄ N, (C₂ H₄ OH)₃ NH, (C₂ H₅)₂ NH₂, (C₂ H₅)(C₃H₆ OH)NH₂, (C₂ H₅)(C₂ H₄ OH)₃ N and the like. Hydroxides of thesesubstituted or unsubstituted ammoniums are usually strong alkalinesubstances, and easily form silicates when reacted with silicic acid orcolloidal silica. The examples of silicates of these substitutedammoniums are silicates of methylammonium, dimethylammonium,dimethyldiethanolammonium, triethanolammonium, tetraethanolammonium,diethylammonium, ethylpropanolammonium and ethyltriethanolammonium. Suchsilicates may be used solely or in the form of a mixture.

An alkali silicate solution with a Si₂ O/M₂ O mole ratio of less than 1does not sufficiently modify the surface layer of the cement structurefrom the practical view point. An alkali silicate solution with a SiO₂/M₂ O mole ratio of more than 50 does not show a sufficient permeabilityinto the structure, due to too high content of colloidal silica in theagent.

An alkali silicate solution of a SiO₂ content less than 1 weight % doesnot sufficiently increase the strength of cement structure surface layerwhen applied on it, and an alkali silicate solution of a SiO₂ contentmore than 50 weight % is not satisfactory in its stability and oftencauses gelation. Even if such defects would not be observed, suchsolution of too high concentration makes the quality of the resultingmodified layer uneven. A preferable SiO₂ content of the alkali silicatesolution lies in the range of from 5 to 30 weight %.

The alkali silicate solution with the SiO₂ /M₂ O mole ratio of 1 toabout 4 can be prepared by dissolving an alkali silicate in water or byadding an alkali to form said salt in colloidal silica dispersion and ifnecessary heating. The alkali silicate solution with the SiO₂ /M₂ O moleratio of higher than 4 is a liquid wherein colloidal silica co-exists ina dispersion state. Such alkali silicate solution with a higher moleratio can be prepared by adding an alkali silicate or alkali hydroxideinto a colloidal silica dispersion and if necessary heating, ordealkalizing an alkali silicate solution according to a cation exchangemethod or the like and if necessary adding an alkali to form said saltto stabilize the dispersion. Colloidal silica of smaller particle sizeis preferable for the alkali silicate solution with the SiO₂ /M₂ O moleratio of higher than 4, particularly higher than 7. The particle size ispreferably less than 50 μm and more preferably less than 20 μm.According to the invention, it is preferable to use a lithium silicatesolution with a SiO₂ /M₂ O mole ratio of 2 to 7 and a low colloidalsilica content.

The sodium naphthalenesulfonate-formaldehyde condensate used for theinvention is a polymer usually represented by formula ##STR1## wherein nis an integral of 1 to 100. Such a condensate is easily and commerciallyavailable. It is preferable that the condensate has a polymerizationdegree ranging from 3 to 50. As aforesaid, the agent according to theinvention comprises 100 parts by weight of said alkali silicate solutionand 0.01 to 5 parts by weight of such condensate. The agent having thecondensate content of less than 0.01 part by weight has not an excellentpermeability into the cement structure. The agent having the condensatecontent of more than 5 parts by weight is of a low stability, and theviscosity of the agent is increased with lapse of time and gelation isoften caused. Preferable content of the condensate ranges from 0.02 to 1part by weight.

The agent of the invention can easily be prepared by mixing the alkalisilicate solution with the condensate in said ratio and thenhomogenizing the same. The agent may comprise coloring agent,stabilizer, viscosity regulating agent and any of other components, inaddition to said two indispensable components. The agent may be used asa paint by adding paint components thereto to form a decorated surfaceon the cement structures.

The agent may be applied to any of hardened cement structures such as ahardened cement structure, hardened mortar structure, hardened concretestructure, calcium silicate board and the like. The structure may be ofany configuration. The agent can be applied also to a deterioratedcement structure such as the wall of concrete structure and mortar walland, deteriorated cement products, such as a concrete surface which wasformed by insufficient curing due to a dry out, freezing or penetrationof lignin, or a concrete surface which has been deteriorated byweathering or fire.

The agent may be permeated into the cement structure from its outersurface with use of any conventional method, for instance by brushing,rolling, spraying or the like, or by soaking. The treated cementstructure is then left to stand in air or positively dried to formmodified surface layer over a sufficient depth. The modified surfacelayer has a compacted structure, increased strength and hardness, aswell as an excellent resistance to water and weathering. Even if a shockis affected on the modified surface to cause a certain damage thereon, anon-modified layer would not so readily be exposed, since the modifiedlayer has a sufficient thickness. Further, if necessary, a protectivepaint may be applied on the modified surface to obtain a cementstructure with a decorative or protective surface. Moreover, a cement,mortar or concrete structure with a surface deteriorated by weatheringor fire can be repaired by applying the agent on the deterioratedsurface to impregnate the same with said agent, leaving to stand in airor positively drying the treated surface, applying thereon a freshlyprepared cement paste, mortar or concrete and curing the same. Accordingto this method, the freshly formed cement material layer firmly binds onthe strengthened modified layer. On the contrary, the conventionalmodifying agent can not provide a modified layer over a sufficientthickness and with a sufficient strength and thus such an accident cannot be avoided that an inner un-modified layer is damaged by a shockagainst an outer surface to cause a peeling off of the freshly formedcement material layer attached by a thin already modified layer.

It has not sufficiently been elucidated why the agent according to theinvention can permeate from an outer surface of the cement structureinto deeper area thereof, but shall be estimated as follows. Inaccordance with the prior art processes, a free calcium content in thehardened cement structure contacts with an alkali silicate solutionentering into the structure through fine bores thereof to cause agelation, so that deeper permeation of the alkali silicate solution isprevented. While in accordance with the invention, said free calcium iscatched by the co-existing condensate of sodium naphthalenesulfonate andformaldehyde and thus the viscosity increase or gelation of the alkalisilicate solution can be avoided to allow permeation of the silicatesolution into deeper area of said structure. It was surprised, however,that the agent according to the invention and comprising the alkalisilicate solution and the condensate shows an excellent stability andpermeability, since water soluble compounds with sulfonic acid radicalother than said condensate, for instance sodium alkylbenzenesulfonate,sulfonated melamine-formaldehyde condensate and the like increaseviscosity of the alkali silicate solution or make same unstable to showno desired effect.

The invention will now be further explained in detail, with reference toExamples and Comparative Examples.

EXAMPLES 1 to 4

In each 1000 g aqueous solution of lithium silicate, sodium silicate,potassium silicate and tetraethanolammonium silicate having SiO₂ /M₂ Omole ratio of 3.5 and SiO₂ content of 10 weight %, 1 g of 30% aqueoussolution of sodium naphthalenesulfonate-formaldehyde condensate havingdegree of polymerization of 10 was added and then stirred to prepare 4agents according to the invention. Each of the agents was sealinglystored at 40° C. for 6 minutes to find that each agent remains in stablestate and shows neither viscosity increase nor isolation.

Mortar blocks with a cement/sand ratio of 1/3 and size of 4×4×16 cm wereleft to stand in a carbon dioxide atmosphere to neutralize the same.Each of the resulting blocks was soaked in each of said agent solutionsfor 1 hour, picked up and then dried in air at room temperature for 1day. Each of the treated blocks was chopped and a solution ofphenolphthalein was blown on the chopped surface to give a colour markto the area where the agent was permeated and measure the permeateddepth. Results are shown in following Table 1.

COMPARATIVE EXAMPLES 1 to 4

Tests similar to those in Examples 1 to 4 were carried out, exceptingthat the condensate of sodium naphthalenesulfonate-formaldehyde is notadded to each agent. Results are shown in following Table 1.

EXAMPLES 5 to 8

Tests similar to those in Examples 1 to 4 were carries out, exceptingthat calcium silicate boards, each having a specific gravity of 0.8 anda size of 2×4×4 cm were used as the cement structures in lieu of themortar blocks. Resulsts are shown in following Table 1.

COMPARATIVE EXAMPLES 5 to 8

Tests similar to those in Comparative Examples 1 to 4 were carried out,excepting that calcium silicate boards as employed in Examples 5 to 8were used in lieu of the mortar blocks. Results are shown in followingTable 1.

                  TABLE 1                                                         ______________________________________                                               Alkali silicate                                                                           Cement   Permeated depth                                          in Agent    Material (mm)                                              ______________________________________                                        Example                                                                       1        lithium silicate                                                                            mortar   5                                                                    block                                                  2        sodium silicate                                                                             mortar   3                                                                    block                                                  3        potassium silicate                                                                          mortar   2                                                                    block                                                  4        tetraethanol- mortar   2                                                      ammonium      block                                                           silicate                                                             5        lithium       calcium  20                                                     silicate      silicate                                                                      board                                                  6        sodium silicate                                                                             calcium  20                                                                   silicate                                                                      board                                                  7        potassium silicate                                                                          calcium  10                                                                   silicate                                                                      board                                                  8        tetraethanol- calcium  10                                                     ammonium      silicate                                                        silicate      board                                                  Comparative                                                                   Example                                                                       1        lithium       mortar   2                                                      silicate      block                                                  2        sodium silicate                                                                             mortar   1                                                                    block                                                  3        potassium     mortar   1                                                      silicate      block                                                  4        tetraethanol- mortar   1                                                      ammonium      block                                                           silicate                                                             5        lithium       calcium  5                                                      silicate      silicate                                                                      board                                                  6        sodium silicate                                                                             calcium  3                                                                    silicate                                                                      board                                                  7        potassium     calcium  2                                                      silicate      silicate                                                                      board                                                  8        tetraethanol- calcium  2                                                      ammonium      silicate                                                        silicate      board                                                  ______________________________________                                    

EXAMPLE 9

In 1000 g aqueous solution of lithium silicate having SiO₂ /M₂ O moleratio of 3.0 and SiO₂ content of 10 weight %, 3 g of the sodiumnaphthalenesulfonate-formaldehyde condensate same with that as used forExamples 1 to 4 were added and the resulting mixture was stirred toprepare the agent according to the invention.

On a concrete structure with a surface deteriorated by having left tostand at outdoor for about 10 years, the agent was applied continuouslyuntil an absorption of the agent into the structure stops and then acertain amount of the agent remains on the structure, without absorbedtherein. 600 g/m² of the agent was required therefor. The structure wasdried in air for 1 day. After having applied on the treated surface anacrylic emulsion paint and then sufficiently cured the same, a tensiontesting element was adhered on the coated surface with use of a strongadhesive and then the structure was subjected to a tension test to findthat tensile strength of the resulting concrete was about 15 Kg/cm² andthe depth of the disintegrated layer was 10 mm from the concretesurface.

COMPARATIVE EXAMPLE 9

A test similar to that in Example 9 was carried out, excepting that thecondensate of sodium naphthalenesulfonate and formaldehyde was not addedin the agent. In this case, an amount of agent permeated in thestructure was 400 g/m². Tension test shows that the tensile strength isabout 15 Kg/cm² but a depth of the disintegrated layer was 4 mm.

COMPARATIVE EXAMPLES 10 to 13

A modifying agent was prepared in the manner similar to those inExamples 1 to 4, excepting that a surfactant ofpolyoxyethylenenonylphenol ether was used in lieu of the condensate ofsodium naphthalenesulfonate and formaldehyde. The freshly prepared agentwas applied on the structure as in Examples 1 to 4 to measure permeatingdepth. Results are shown in following Table 2.

The above agent was left to stand at 40° C. for about 2 weeks to findthat the agent causes an increase in its viscosity and an isolation ofcomponents.

COMPARATIVE EXAMPLES 14 to 17

Tests were carried out in the manner similar to those in Examples 1 to4, excepting that a fluoro surfactant (Trade Name "EFTOP EF-112" sold byTohoku Hiryo Kabushiki Kaisha, Japan) was used in lieu of the condensateof sodium naphthalenesulfonate and formaldehyde. Results are shown infollowing Table 2.

COMPARATIVE EXAMPLES 18 to 20

Tests were carried out in the manner similar to those in Examples 1 to4, excepting that sodium toluensulfonate solution or sulfonatedmelamine-formaldehyde condensate solution was used in lieu of the sodiumnaphthalenesulfonate-formaldehyde condensate. Results are shown infollowing Table 2.

                  TABLE 2                                                         ______________________________________                                                                           Permeated                                  Comparative                                                                            Alkali silicate           depth                                      Example  in Agent        Surfactant                                                                              (mm)                                       ______________________________________                                        10       lithium silicate                                                                              EOP       2                                          11       sodium silicate "         1                                          12       tetraethanolammonium                                                                          "         1                                                   silicate                                                             13       potassium silicate                                                                            "         1                                          14       lithium silicate                                                                              F         2                                          15       sodium silicate "         1                                          16       potassium silicate                                                                            "         1                                          17       tetraethanolammonium                                                                          "         1                                                   silicate                                                             18       lithium silicate                                                                              TS        1.5                                        19       lithium silicate                                                                              SMF       1.5                                        20       sodium silicate "         1                                          ______________________________________                                         In the Table:                                                                 EOP: polyoxyethylenenonylphenol ether                                         F: fluoro surfactant (EFTOP EF112)                                            TS: sodium toluenesulfonate                                                   SMF: sulfonated melamineformaldehyde condensate                          

EXAMPLE 10

A test similar to that in Example 9 was carried out, excepting that inlieu of the acrylic emulsion paint, a mortar with sand/cement weightratio of 2/1 and containg 7.5 weight % of SBR latex in dried contentbased on the cement was applied on the deteriorated structure surface in2 mm thickness. The resulting structure was left to stand for about 1month in atmosphere. A tension testing element was adhered on thestructure surface with use of a strong adhesive and then the structurewas subjected to a tension test to find that tensile strength of theresulting structure was about 15 Kg/cm² and the depth of thedisintegrated layer was 10 mm from the surface of the concrete.

COMPARATIVE EXAMPLE 21

A test similar to Example 10 was carried out, excepting that thecondensate of sodium naphthalenesulfonate-formaldehyde was not added tothe basic agent. In this case, the tensile strength was about 15 Kg/cm²but the depth of the disintegrated layer was 4 mm from the surface ofthe concrete.

What we claimed is:
 1. A method for modifying a surface layer of cementstructures, which comprises steps of applying on surface of thestructure an agent comprising 100 parts by weight of an alkali silicatesolution and 0.01 to 5 parts by weight of a condensate of sodiumnaphthalenesulfonate and formaldehyde, in which said alkali silicatesolution has a SiO₂ /M₂ O mole ratio of 1 to 50, wherein M represents analkali metal atom, or a substituted or unsubstituted ammonium cationicradical, and has a SiO₂ content of 1 to 50 weight %, impregnating thesurface layer of said structure with said agent, and then leaving tostand or positively drying the treated structure.
 2. The method asclaimed in claim 1, wherein said alkali silicate is any of silicates oflithium, potassium, sodium, methylammonium, dimethylammonium,dimethyldiethanolammonium, triethanolammonium, tetraethanolammonium,diethylammonium, ethylpropanolammonium and ethyltriethanolammonium, orany combination of such silicates.
 3. The method as claimed in claim 1,wherein said condensate has a polymerization degree ranging from 1 to100.
 4. The method as claimed in claim 1, wherein said agent comprises100 parts by weight of lithium silicate solution and 0.02 to 1 part byweight of said condensate having a polymerization degree ranging from 3to 50, in which said lithium silicate solution has a SiO₂ /M₂ O moleratio of 2 to 7 and has a SiO₂ content of 5 to 30 weight %.
 5. Themethod as claimed in claim 1, wherein said cement structure is made fromany of hardened cement, mortar, concrete and calcium silicate board. 6.The method as claimed in claim 5, wherein said structure is in the formof wall.
 7. The method as claimed in claim 6, wherein said wallstructure has a deteriorated surface layer.
 8. A method for repairing adeteriorated surface layer of cement structures, which comprises stepsof applying on the deteriorated surface of the cement structure an agentcomprising 100 parts by weight of an alkali silicate solution and 0.01to 50 parts by weight of a condensate of sodium naphthalenesulfonate andformaldehyde, in which said alkali silicate solution has a SiO₂ /M₂ Omole ratio of 1 to 50, wherein M represents an alkali metal atom, or asubstituted or unsubstituted ammonium cationic radical, and has a SiO₂content of 1 to 50 weight %, impregnating the surface layer of saidstructure with said agent, leaving to stand or positively drying thetreated structure, applying a freshly prepared cement material on thetreated surface of said structure, and then curing the applied cementmaterial.
 9. The method as claimed in claim 8, wherein said alkalisilicate is any of silicates of lithium, potassium, sodium,methylammonium, dimethylammonium, dimethyldiethanolammonium,triethanolammonium, tetraethanolammonium, diethylammonium,ethylpropanolammonium and ethyltriethanolammonium, or any combination ofsuch silicates.
 10. The method as claimed in claim 8, wherein saidcondensate has a polymerization degree ranging from 1 to
 100. 11. Themethod as claimed in claim 8, wherein said agent comprises 100 parts byweight of lithium silicate solution and 0.02 to 1 part by weight of saidcondensate having a polymerization degree ranging from 3 to 50, in whichsaid lithium silicate solution has a SiO₂ /M₂ O mole ratio of 2 to 7 andhas a SiO₂ content of 5 to 30 weight %.
 12. The method as claimed inclaim 8, wherein said cement structure is made from any of hardenedcement, mortar, concrete and calcium silicate board.
 13. The method asclaimed in claim 12, wherein said structure is in the form of wall.